Capacitance values have conventionally been measured using methods that employ instruments that are bulky, complicated and expensive. Examples are capacitance bridges, impedance meters, oscillator circuits, and other precision instruments, which are typically stand-alone "benchtop" instruments.
Most users, however, prefer to have an instrument that is portable, self-powered, lightweight, inexpensive, and simple to operate. For example, handheld meters that measure electrical properties such as resistance, voltage, and current are available. Such meters are portable, self-powered, lightweight, inexpensive, simple to use and, hence, very popular. It is desirable to have a method and apparatus for measuring capacitance that can be inexpensively incorporated in handheld meters.
FIG. 1 (Prior Art) shows a schematic diagram of an integrating circuit used in the analog-digital converter of a typical handheld meter. This integrating circuit can be incorporated into a capacitance measuring device in accordance with the present invention. Integrating circuit 100 includes an amplifier 110, a R.sub.INT resistor 120, and a C.sub.INT capacitor 130 (sometimes referred to as the feedback capacitor). The output signal of integrating circuit 100 is well known to be given by the equation: ##EQU1## where Vout(t) is the voltage at an output terminal 140 as a function of voltage Vin(t) applied to an input terminal 150. Vin(0) is the initial voltage across C.sub.INT capacitor 130.